Maxima Function
cardinality (a)
Returns the number of distinct elements of the set a.
cardinality
ignores redundant elements
even when simplification is disabled.
Examples:
(%i1) cardinality ({}); (%o1) 0 (%i2) cardinality ({a, a, b, c}); (%o2) 3 (%i3) simp : false; (%o3) false (%i4) cardinality ({a, a, b, c}); (%o4) 3