*  *  * (1) a day of unemployment with respect to any employee, means a calendar day on which he is able to work and is available for work and with respect to which *  *  * no remuneration is payable or accrues to him *  *  * and (2) a “day of sickness”, with respect to any employee, means a calendar day on which because of any physical, mental, psychological, or nervous injury, illness, sickness, or disease he is not able to work, or, with respect to a female employee, a calendar day on which, because of pregnancy, miscarriage, or the birth of a child, (i) she is unable to work or (ii) working would be injurious to her health, and with respect to which *  *  * no remuneration is payable or accrues to him *  *  * Provided, further, That any calendar day on which no remuneration is payable to or accrues to an employee solely because of the application to him of mileage or work restrictions agreed upon in schedule agreements between employers and employees or solely because he is standing by for or laying over between regularly assigned trips or tours of duty shall not be considered either a day of unemployment or a day of sickness. (Section 1(k), Railroad Unemployment Insurance Act)