diff --git a/base/special/ahaversin/README.md b/base/special/ahaversin/README.md
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+* * *
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+## C APIs
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+### Usage
+
+```c
+#include "stdlib/math/base/special/ahaversin.h"
+```
+
+#### stdlib_base_ahaversin( x )
+
+Compute the [inverse half-value versed sine][archaversine] of a double-precision floating-point number (in radians).
+
+```c
+double out = stdlib_base_ahaversin( 0.0 );
+// returns 0.0
+```
+
+If `x < 0`, `x > 1`, or `x` is `NaN`, the function returns `NaN`.
+
+```c
+double out = stdlib_base_ahaversin( -3.14 );
+// returns NaN
+```
+
+The function accepts the following arguments:
+
+- **x**: `[in] double` input value.
+
+```c
+double stdlib_base_ahaversin( const double x );
+```
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+### Examples
+
+```c
+#include "stdlib/math/base/special/ahaversin.h"
+#include
+
+int main( void ) {
+ const double x[] = { -2.0, -1.6, -1.2, -0.8, -0.4, 0.4, 0.8, 1.2, 1.6, 2.0 };
+
+ double v;
+ int i;
+ for ( i = 0; i < 10; i++ ) {
+ v = stdlib_base_ahaversin( x[ i ] );
+ printf( "ahaversin(%lf) = %lf\n", x[ i ], v );
+ }
+}
+```
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