a question of Chains of Implicit Rules

[ali hagigat]

10.4 Chains of Implicit Rules
If the file ‘n.c’ exists, or is mentioned in the makefile, no special
searching is required:
make finds that the object file can be made by C compilation from ‘n.c’;
later on, when
considering how to make ‘n.c’, the rule for running Yacc is used.
Ultimately both ‘n.c’
and ‘n.o’ are updated.
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"later on, when considering how to make ‘n.c’, the rule for running
Yacc is used", what does it mean? Would you please give an example.