  PGA, short for ProGram Algebra, describes sequential programs as finite or
infinite (repeating) sequences of instructions. The semigroup C of finite
instruction sequences was introduced as an equally expressive alternative to
PGA. PGA instructions are executed from left to right; most C instructions come
in a left-to-right as well as a right-to-left flavor. This thesis builds on C
by introducing an alternative semigroup Cg which employs label and goto
instructions instead of relative jump instructions as control structures. Cg
can be translated to C and vice versa (and is thus equally expressive). It is
shown that restricting the instruction sets of C and Cg to contain only
finitely many distinct jump, goto or label instructions in either or both
directions reduces their expressiveness. Instruction sets with an infinite
number of these instructions in both directions (not necessarily all such
instructions) do not suffer a loss of expressiveness.
