reserve a,b,k,m,n,s for Nat;
reserve c,c1,c2,c3 for Complex;
reserve i,j,z for Integer;
reserve p for Prime;
reserve x for object;
reserve f,g for complex-valued FinSequence;
reserve a,b,x,y for Real;

theorem :: Problem 198 c
  for a,x,y being Complex holds x|^1 - y|^1 = a iff x = a+y;
