Description: Define the restriction of a class. Definition 6.6(1) of TakeutiZaring
p. 24. For example, the expression ` ( exp |`RR ) (used in
reeff1 ) means "the exponential function e to the x, but the exponent
x must be in the reals" ( df-ef defines the exponential function,
which normally allows the exponent to be a complex number). Another
example is ( F = { <. 2 , 6 >. , <. 3 , 9 >. } /\ B = { 1 , 2 } ) ->
` ( F |`B ) = { <. 2 , 6 >. } ( ex-res ). We do not introduce a
special syntax for the corestriction of a class: it will be expressed
either as the intersection ( A i^i ( _V X. B ) ) or as the converse
of the restricted converse (see cnvrescnv ). (Contributed by NM, 2-Aug-1994)