code: private WyalFile.Stmt and(WyalFile.Stmt lhs, WyalFile.Stmt rhs) {
  		if (lhs == null) {
  			return rhs;
  		} else if (rhs == null) {
  			return rhs;
  		} else {
  			return new WyalFile.Stmt.Block(lhs, rhs);
  		}
  	}
docs: Construct a conjunction of two expressions
  
  @param lhs
  @param rhs
  @return