X5211 : %THEOREM%X5211 is a theorem.
y(OA) = SETUNION .LAMBDA z(OA) EXISTS x(A) .y x AND z = [= x]
All rules and commands, including ADVICE, are allowed.
Only book theorems may be ASSERTed as lemmas without proof.
For a complete list of book theorems, type PROBLEMS.
No more help available. Sorry.
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