Theory of Machine
The inversion of a mechanism is

Obtained by reversing the input and output motion
Turning its upside down
Changing of a higher pair to a lower pair
Obtained by fixing different links in a kinematic chain

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Theory of Machine
The relation l = (2/3).(j + 2) apply only to kinematic chains in which lower pairs are used. This may be used to kinematic chains in which higher pairs are used, but each higher pair may be taken as equivalent to

Two lower pairs and two additional links
Two lower pairs and one additional link
Any one of these
One lower pair and two additional links

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