theorem Th93:
  A ** (B /\ C) c= (A**B) /\ (A**C)
proof
  let a;
  assume a in A**(B/\C);
  then consider c,c1 such that
A1: a = c*c1 and
A2: c in A and
A3: c1 in B/\C;
  c1 in C by A3,XBOOLE_0:def 4;
  then
A4: c*c1 in A**C by A2;
  c1 in B by A3,XBOOLE_0:def 4;
  then c*c1 in A**B by A2;
  hence thesis by A1,A4,XBOOLE_0:def 4;
end;
