Sometimes we have to test complicated logical conditions. Complex conditions can often be expressed in terms of more elementary conditions by means of the logical connectives "AND", "OR", and "NOT". Although Refal Plus does not provide logical connectives explicitly, they can be easily represented by other constructs.
Suppose we have two conditions and must determine whether both of them are satisfied.
If both conditions are represented by paths
If the first condition is represented by a source
And, finally, if both conditions are represented by result expressions
Suppose we have two conditions and must determine whether one (or both) of them are satisfied.
If both conditions are represented by paths
Suppose we have a condition represented by a path
which is an abbreviation to the path
In cases where the condition is represented by a source
which is an abbreviation to the path
In both cases we take the opportunity of omitting the rests consisting of a single comma.