Usage:
<interchange_permutation a b c
sets c equal to the
permutation matrix of the permutation taking the set
A x B (where a,b are the cardinalities of A,B) in lex order to the
same set in the order that corresponds to the lex order
on B x A
Parameters:
a,b = positive integers, the size of the sets A,B
Output values:
an invertible ab x ab matrix
It might be more efficient to use the contract command
than the lift command as is done here