\input texinfo

@macro usubsec {label, titl}

@set lb \label\
@set tl \titl\
@ifclear usubsec-no-label
   @unnumberedsubsec @value{lb} @ @value{tl}
@end ifclear

@ifset usubsec-no-label
  @unnumberedsubsec @value{tl}
@end ifset

@end macro

@usubsec{16D,
Utilisation of Rapid Computations}

@set usubsec-no-label

@usubsec{16D,
Utilisation of Rapid Computations}

@bye