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 | 3.9.2 Tracing of proceduresSetting theTRACEvariable to 1 (resp. 3) results in reporting of
all procedure entries and exits (resp. together with line numbers).
IfTRACEis set to 4,Singulardisplays each line before its interpretation and waits for the RETURN
key being pressed.See TRACE var. Example: 
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