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*Proposition:*
If `A` and `B` are disjoint with sizes `m` and `n`,
respectively, then the size of their union is `m`+`n`:

forallA,B,minN,ninN:( AintersectionB=0/\ |A| =m/\ |B| =n) => |AunionB| =m+n.

The size of the Cartesian product of two sets is the product of their sizes:

forallA,B,minN,ninN:(| A| =m/\ |B| =n) => |AxB| =m*n.

Author: Wolfgang Schreiner

Last Modification: December 7, 1999