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Added begin-exp to parse and unparse. Syntax-expanded begin-exp to an application of a lambda expression with no arguments.
Added cond expressions to parse and unparse. Still need to syntax-expand them.
Added syntax-expansion for cond expressions
Added and and or expressions, and syntax-expansion for them
Added case expressions and their syntax-expansions. Also fixed a syntax-expansion bug where if-true-exp tried to expand to an if-exp.
code understood merging and then working on while