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This corresponds to, before performing the transformations and describing the object, to declare the start and end of operations in some way.
SUBROUTINE PUSH
indicates the start of an occurrence of an object (it stacks a unit matrix).
SUBROUTINE PREPAR
must imperatively terminate the sequence describing the transformations and precede the sequence describing the object (it evaluates the transformation matrix).
SUBROUTINE PULL
must imperatively follow the sequence describing an object (returns to the called object's space). A correct calling sequence for an object must therefore have the following form:
CALL PUSH DEFINITION OF THE TRANSFORMATIONS CALL PREPAR SEQUENCE DESCRIBING THE OBJECT CALLED CALL PULL
The PUSHes and PULLs can be nested up to 8 levels in the following manner:
CALL PUSH ..... CALL PREPAR ..... CALL PUSH ..... CALL PREPAR ..... CALL PULL ..... CALL PULL
SUBROUTINE RAZPSK
is used to set the transformation stack pointer to 0 (done automatically in DEVICE).