:: deftheorem Def12 defines the_Tree_of CGAMES_1:def 12 :
for g being ConwayGame
for b₂ being set holds
( b₂ = the_Tree_of g iff for z being set holds
( z in b₂ iff ex f being ConwayGameChain st
( f . 1 = z & f . (len f) = g ) ) );