diff --git a/notebooks/7_ptypes.jl b/notebooks/7_ptypes.jl
new file mode 100644
index 0000000..28d6829
--- /dev/null
+++ b/notebooks/7_ptypes.jl
@@ -0,0 +1,533 @@
+### A Pluto.jl notebook ###
+# v0.19.46
+
+using Markdown
+using InteractiveUtils
+
+# ╔═╡ e248ec9e-7b3c-11ef-3434-b1e6fc44ac3b
+using PlutoUI
+
+# ╔═╡ cb79cfad-9b8c-4017-ba7c-9cebcebc84f7
+TableOfContents(title="📚 Table of Contents", indent=true, depth=4, aside=true)
+
+# ╔═╡ 144c7859-9880-4d8a-af4a-3f0d4e77bc46
+md"""
+# 1. Views (Performance)
+"""
+
+# ╔═╡ 2b0b302c-f474-4964-b88b-e182057cd5db
+M = rand([2,3,5,7,9],3,3)
+
+# ╔═╡ 9d6f60eb-7af4-4986-8946-e5a08868fda4
+A = view(M, 2:3, 1:2)
+
+# ╔═╡ 53ffeb7e-3e60-4c2f-b34a-984a7a7fb2df
+md"""
+# 2. Create a type, what methods are created?
+"""
+
+# ╔═╡ fe8b88e1-05fb-4387-8b04-c329ff4c46f3
+struct C25
+	value::Float64
+end
+
+# ╔═╡ 484b9cd9-2820-471b-85d3-75f23bbd9b61
+C25(1.0)
+
+# ╔═╡ 61dbdaaa-cc20-4bc9-a80c-5f4b9be1536a
+md"""
+Note that this **constructor** (a function with the same name as the type that creates objects of that type) was **automatically generated** when we defined the type. We can ask Julia which of these so-called default constructors are provided:
+"""
+
+# ╔═╡ 042e554c-59f7-4107-b958-76adcfcb8800
+display(methods(C25))
+
+# ╔═╡ 4f9f2a79-98e3-4244-81c0-6ad089c1ec57
+C25(true)
+
+# ╔═╡ 64fc97fa-897a-4b03-81ad-e5121c3ccf00
+C25("Philip")
+
+# ╔═╡ 6d46a963-d316-4b95-82a0-a8c8a3f3a050
+convert(Float64, true)
+
+# ╔═╡ 8f6f438d-a2b7-4eb0-b527-cf75e7741418
+C25("3.1")
+
+# ╔═╡ ce9fcfb2-9ab0-445f-beea-907c83a5b88b
+convert(Float64, "3.1")
+
+# ╔═╡ 9c1240da-86e8-4b27-9a49-ec56c632b725
+parse(Float64,"3.1")
+
+# ╔═╡ d27918d5-363a-49c7-a358-5265d35244ab
+md"""
+# 3. convert and Type{T} type selectors
+"""
+
+# ╔═╡ 06df76cc-8c6f-4997-b7f0-8bd475f2fa7d
+md"""
+You can define your own convert
+"""
+
+
+# ╔═╡ 406b2aab-a2ea-4540-9f2a-06f2513095b5
+# Base.convert(::Type{Float64}, s::String) = parse(Float64, s)
+
+# ╔═╡ 77349ae4-6c57-40d5-91b1-db353c7f2ddb
+md"""
+::Type{Float64}
+means that the second argument s is a string and the first argument is not a Float64 but is itself a type. See  doc on [ Type{T} type selectors] (https://docs.julialang.org/en/v1/manual/types/#man-typet-type).
+"""
+
+# ╔═╡ f176edcc-de5e-4cd0-b6dd-428ce3ca302c
+begin
+  h1(::String, s::String) = s
+  h2(T::Type{String}, s::String) = T  
+  h3(T::Type{Number}, s::String) = T 
+end
+
+# ╔═╡ 0d8857b7-747a-4415-b505-aaa3c9110027
+h1("abc","def")
+
+# ╔═╡ 5eed423a-c0fb-449c-a3cc-6ed4f4e7ae7f
+h2(String,"def")
+
+# ╔═╡ fdc2102a-b25a-431e-ba9e-827898b0a421
+h3(Number,"def")
+
+# ╔═╡ c8c00b27-1467-4119-b9c5-3a4050adb047
+isa(3.0, Float64)
+
+# ╔═╡ 29f0fa70-715e-450b-8f24-b83d00399240
+isa(Float64,Type{Float64})
+
+# ╔═╡ 67a7ac4f-89cb-4fb1-99b5-23c7efae24e8
+Type{Float64} <: DataType
+
+# ╔═╡ f22b8320-1751-4920-995e-3dd762f1d884
+md"""
+# 4. getfield
+"""
+
+# ╔═╡ 3049e587-c25b-4926-8aa1-cf3781a1e642
+fieldnames( C25 )
+
+# ╔═╡ 55d8bbc7-5d0e-495a-b371-34cffb9d4884
+C25(3).value
+
+# ╔═╡ a35181c6-5040-4cbb-9cb0-643c2a5b8593
+getfield(C25(3),:value)
+
+# ╔═╡ 13237b9e-edc6-4288-a51f-146b3e3d5252
+getfield(C25(3),1)
+
+# ╔═╡ f1e944fe-e8ee-47ca-bdb8-ffff8c245cdd
+md"""
+# 5. constructors with conditions
+"""
+
+# ╔═╡ 1a57c6a7-105e-4bed-acd4-0c4250d410f9
+md"""
+In this example, we also illustrate [short circuit evaluation](https://docs.julialang.org/en/v1/manual/control-flow/#Short-Circuit-Evaluation)
+
+Here we have used so-called "short-circuit" evaluation: && can be thought of as an if...then, while || is unless... (i.e. if not ... then).
+"""
+
+# ╔═╡ ac317618-c293-41cf-a5de-a123b1674e7f
+struct C25v2
+    value::Float64
+    
+    function C25v2(x)
+    
+        x < 0 && throw(ArgumentError("Negative value not allowed."))
+        
+        new(x)
+    end
+end
+
+# ╔═╡ 31fd9ece-a5c2-4072-b1ef-3d33268dc678
+C25v2(-1)
+
+# ╔═╡ a7d8ce7b-50db-4503-972f-0b0e17e340ee
+md"""
+# 6. What if we don't want to nail down the type?
+"""
+
+# ╔═╡ 9f20ba44-658a-42d3-8baa-e25b4a4d86b0
+md"""
+sometimes it's okay to do this, but one can do better
+"""
+
+# ╔═╡ a78c8fbf-5555-4f10-9491-5f2af68c632e
+struct C25v3
+	v
+end
+
+# ╔═╡ 93f6dacc-ebc8-4d0b-ab5f-10c9ec395a2d
+md"""
+# 7. Parametric Types
+"""
+
+# ╔═╡ b6b34a07-ffb1-4f62-8b71-3f6fb56f11fa
+struct C25v4{T}
+	v::T
+end
+
+# ╔═╡ dab97bb1-aec9-4ff7-8e20-24725be751c5
+C25v4(3)
+
+# ╔═╡ 0720bbc9-c47a-4dcf-b43d-27c06354cdc2
+C25v4(2.54)
+
+# ╔═╡ b2d48852-3ec7-4e5c-8363-b7325ae895fe
+C25v4( rand(3,3))
+
+# ╔═╡ 3e09c429-4daf-4bc0-92fa-97ef43dbaf68
+C25v4( C25v4(7))
+
+# ╔═╡ e4bb130f-9e98-4afe-85e8-38f7483b62db
+md"""
+# 8. Adding Conditions to types
+"""
+
+# ╔═╡ 0d789338-f2b9-4765-a7e9-d33ee416f560
+struct C25v5{ T<:Real }
+	v::T
+end
+
+# ╔═╡ af52a273-c1bc-46af-a0a3-ff826b324cd6
+C25v5(3)
+
+# ╔═╡ e65b158d-7c54-4b9c-895b-cdaaadde20ee
+C25v5("hello")
+
+# ╔═╡ 00000000-0000-0000-0000-000000000001
+PLUTO_PROJECT_TOML_CONTENTS = """
+[deps]
+PlutoUI = "7f904dfe-b85e-4ff6-b463-dae2292396a8"
+
+[compat]
+PlutoUI = "~0.7.60"
+"""
+
+# ╔═╡ 00000000-0000-0000-0000-000000000002
+PLUTO_MANIFEST_TOML_CONTENTS = """
+# This file is machine-generated - editing it directly is not advised
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+"""
+
+# ╔═╡ Cell order:
+# ╠═e248ec9e-7b3c-11ef-3434-b1e6fc44ac3b
+# ╠═cb79cfad-9b8c-4017-ba7c-9cebcebc84f7
+# ╠═144c7859-9880-4d8a-af4a-3f0d4e77bc46
+# ╠═2b0b302c-f474-4964-b88b-e182057cd5db
+# ╠═9d6f60eb-7af4-4986-8946-e5a08868fda4
+# ╟─53ffeb7e-3e60-4c2f-b34a-984a7a7fb2df
+# ╠═fe8b88e1-05fb-4387-8b04-c329ff4c46f3
+# ╠═484b9cd9-2820-471b-85d3-75f23bbd9b61
+# ╟─61dbdaaa-cc20-4bc9-a80c-5f4b9be1536a
+# ╠═042e554c-59f7-4107-b958-76adcfcb8800
+# ╠═4f9f2a79-98e3-4244-81c0-6ad089c1ec57
+# ╠═64fc97fa-897a-4b03-81ad-e5121c3ccf00
+# ╠═6d46a963-d316-4b95-82a0-a8c8a3f3a050
+# ╠═8f6f438d-a2b7-4eb0-b527-cf75e7741418
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