Use intermediate representation

[mristin]

Current immediate representation (IR) is crude and the strategies are directly inferred on abstract syntax tree (AST). This approach is quite limiting as it is difficult to reason about better pattern matching at a higher level of abstraction.

Instead of direct matching, introduce three different IRs:

1. AST of the contracts -> constraint base which contains all the relevant preconditions in an interpretable form. This might be AST, but can be also a different representation; it needs to be further explored.
2. Dependency graph which represents multi-argument constraints and how they are related.
3. Flow graph that covers material implications (not A or B which is equivalent to A implies B) and disjunctions (A or B).

This needs more thinking and a literature survey. It is written here as a note for further discussion.