library Tree

spec Tree =

free type Colour ::= a | b | c

free type Tree ::= Node(Colour) | Tree(Tree;Tree)

op swap : Tree -> Tree

forall c:Colour; t,t1,t2:Tree

. swap (Node(c))=Node(c)

. swap (Tree(t1,t2)) = Tree(swap(t2),swap(t1))

end