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A decision (also called branch) has a single incoming flow and several guarded out-bound flows.
Each outbound flow has a guard: a Boolean condition placed inside square brackets.
Thus, a guard on the decision can be true or false.
Activity can take only one of the outbound flows: the guards are mutually exclusive.
Using [else] as a guard indicates that its flow used if all other guards are false.
A merge has multiple input flows and a single output.
A merge marks the end of conditional behavior started by a decision.
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