#$overrides is used when the assertions involved are general rules (axioms with quantifiers) and where those assertions will produce contradictory results in some situations. #$overrides makes it possible to resolve the contradictions by giving one of the assertions priority over the other.
To take a trite example:
P1 = "If something is a penguin, it can't fly."
P2 = "If something is a bird, it can fly."
P1 overrides P2. more ... about Default Reasoning
#$CycLExpression CycL expressions
The collection of all syntactically well-formed expressions in the CycL language. This includes constants, variables, non-atomic terms, formulas, sentences, etc. Since the CycL syntax allows any CycL expression to be used as a term, #$CycLExpression is actually coextensional with #$CycLTerm (q.v.). Note that #$CycLExpression, like most #$CycLExpressionTypes, is a #$quotedCollection (q.v.).
more ... about Expressions
#$arg1Format arg 1 format
An instance of #$ArgFormatPredicate (q.v.) used to place a particular #$Format (q.v.) constraint on the first (or arg1 ) argument-place of a given predicate. (#$arg1Format PRED FORMAT) means that PRED's arg1 is constrained to FORMAT. See the reified instances #$Format for further details.
direct instance of: #$OpenCycDefinitionalPredicate #$MacroRelation #$IntangibleObjectRelatingPredicate #$GeneralEntryFormatPredicate #$ArgFormatBinaryPredicate
#$arg2Format arg 2 format more ... about Entry Format
The ``arg-genls'' predicates are another way (besides ``arg-isa'') to constrain the arguments of relations. Use of these predicates is optional and frankly not even very common. Of course, one can state more complicated sorts of constraints than ``arg-isa'' and ``arg-genls'' by asserting a longer Cyc formula, but these two types of short-cuts handle the most common cases.
#$arg1Genl arg 1 genl more ... about Argument Genl
Argument-type predicates are used to constrain the arguments of all relations, including predicates and functions. For each argument position that a relation takes, it must have an ``arg-isa'' for that position, even if it also has an ``arg-genls'' for the same position.
#$arg1Isa arg 1 isa more ... about Argument Type