Don't copy an immutable digraph when adding zero vertices#346

Merged

james-d-mitchell merged 1 commit intodigraphs:stable-1.3from wilfwilson:improve-opers

Nov 18, 2020

+18-15

Commits on Nov 18, 2020

oper.gi: don't copy imm digraphs to add 0 vertices
wilfwilson
committed