The logical operators allow complex queries to be constructed out of simpler ones using the standard boolean connectives and, or and not. These may be abbreviated by the symbols "&", "|" and "!" respectively. Parentheses (brackets) may be used to alter the precedence of the operators. For convenience, a comma may also be used for boolean disjunction.
The atom expression is evaluated for each atom, hence protein and backbone selects protein bacbone atoms, not the protein and [nucleic] acid backbone atoms!
Examples: backbone and not helix within( 8.0, ser70 ) not (hydrogen or hetero) not *.FE and hetero 8, 12, 16, 20-28 arg, his, lys