3. A benefit is paid to a civil servant who is physically or mentally disabled and who does not receive a disability pension in accordance with subparagraph 3 of the first paragraph of section 56 of the Act respecting the Civil Service Superannuation Plan (chapter R-12). That supplementary benefit shall be equal to the amount by which the pension which would have been paid if he had been entitled to a pension under that subparagraph exceeds the pension to which he is entitled under the Civil Service Superannuation Plan.