Yes the half-line <b>x</b> <= 4 is a preimage of the goal
[3,4].

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Obviously the velocity must point in the direction of increasing
<b>x</b>.

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Let <b>s</b> be the position sensed by the robot at each instant.
The termination condition is: 

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<b>s</b> >= 3.5.

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With this condition the robot cannot stop before reaching abscissa
3. It cannot pass abscissa 4 without stopping.