createChild
fun ConcurrentExecutionContext.createChild(inferProcedureFromGoals: Boolean = true): ConcurrentExecutionContext
Creates a new ConcurrentExecutionContext descending into ConcurrentExecutionContext.currentGoal as a sub-goal: the new context's ConcurrentExecutionContext.goals become just that goal, its ConcurrentExecutionContext.parent is this context, and its ConcurrentExecutionContext.depth/ ConcurrentExecutionContext.step are incremented by one. Used by StatePrimitiveSelection/StateRuleSelection when a goal is not last-call-optimizable, so it gets its own stack frame to backtrack into.