Checks whether a simplex is a face of another simplex and is in the complex.
Usage
is_face(st, tau, sigma)
Arguments
st
a simplex tree.
tau
a simplex which may contain sigma as a coface.
sigma
a simplex which may contain tau as a face.
Value
boolean indicating whether tau is a face of sigma.
Details
A simplex \(\tau\) is a face of \(\sigma\) if \(\tau \subset \sigma\). This function
checks whether that is true. tau and sigma are sorted before comparison.