filters the list rules by picking out only those rules whose left-hand sides match patt.
picks out rules whose left-hand sides match any of the patti.
- The rules in the list rules can be either -> or :> rules.
- If any of the patti is a rule of the form lhs->rhs, then it is treated the same as lhs.
- If patti is a string, it will also match a symbol whose name is the string.
- FilterRules[rules,Except[patt]] gives all rules except those whose left-hand sides match patt.
Introduced in 2007