40 ILCS 5/15-113.9
A participating employee who was employed by the Illinois Mathematics and Science Academy prior to February 1, 1987 shall be entitled to receive service credit under this System for any period of such employment prior to February 1, 1987 for which the required contributions have been received by this System. If credit for such employment has been granted under any other retirement system governed by this Code, credit for such employment shall not be granted under this System unless (1) the employee so elects in writing prior to April 1, 1987, and (2) the credit granted for such employment in the other retirement system has been terminated, and any employee and employer contributions received therefor by the other retirement system have been transmitted by that retirement system to this System. Such other retirement system shall terminate such credit, and transfer the associated contributions, upon receiving notice of the election from the Board of this System.
40 ILCS 5/15-113.9