SYSML21 — filter not is not supported as shown in the spec examples

Filter expressions using the keyword "not" are not supported as shown in the examples in the spec. The example model views in 7.26.2 ("filter not @SysML::ConnectionUsage" and "expose VehicleDesignModel::**[not @SysML::ConnectionUsage]") do not parse in the pilot implementation as written. However, they do parse when written as "filter not (@SysML::ConnectionUsage)" and "expose VehicleDesignModel::**[not (@SysML::ConnectionUsage)]" respectively.

These example models should be revised to comply with what the language allows. A brief explanation for the required parentheses (e.g., due to the operator precedence rules, not is evaluated before @) would also be helpful.