Hold together local variable and stack state.
Return the bottom element.
Return the bottom element.
Compute the least upper bound of a list of elements.
Compute the least upper bound of a list of elements.
Return the least upper bound of a and b.
Return the least upper bound of a and b.
Return the top element.
Return the top element.
The lattice of type stacks. It is a straight forward extension of the type lattice (lub is pairwise lub of the list elements).