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For every `A`, `B`, `C`, `D` and every
`R` subset `A` x `B`,
`S` subset `B` x `C`, and
`T` subset `C` x `D`, we have:

( R^{-1})^{-1}=R;Ro (SoT) = (RoS) oT;( RoS)^{-1}=S^{-1}oR^{-1}.

*Proof:* see lecture notes (will be discussed later).

Author: Wolfgang Schreiner

Last Modification: October 14, 1999