VSI Pascal expressions consist of  one  or  more  operands  that
  result  in a single value.  If the expression contains more than
  one operand, the operands are separated by operators.   Operands
  include  numbers,  strings,  constants,  variables, and function
  designators.  Operators include arithmetic, relational, logical,
  string, set, and typecase operators.

  VSI  Pascal  recognizes  two  forms  of  expressions:   constant
  expressions  and  run-time  expressions.   Constant  expressions
  result in a value at the time you compile your  program.   These
  expressions   can   include   constants,  constant  identifiers,
  operators, and some predeclared functions.  Run-time expressions
  can only result in a value at the time you execute your program.
  These expressions can include variables, predeclared  functions,
  user-declared   functions,   and   everything  that  a  constant
  expression cannot contain.

  See the "HP Pascal Language Reference Manual"  for  restrictions
  on   constant  expressions  and  information  on  evaluation  of
  expressions in statements.

  Syntax:

    simple-expression [[ {<> | < | <= | = | > | >= | IN}
    simple-expression ]]