There is a rule of “one pension per person” for receiving pension benefits. This means that if a person becomes eligible to receive multiple pensions due to different reasons (e.g. old-age retirement, disability, survivor, etc.), that person will only be able to receive one of them and the payment for the others will be suspended.
For example, Old-age Employees' Pension (old age and retirement are the reasons for this pension) and Disability Employees' Pension (disability is the reason for this pension) have different reasons, and the person must choose which pension to receive.
Note that if there is the amount of suspended pension is increased due to rerision in some cases a person may be able to receive a larger amount by changing the pension they are receiving. In that case of the pension the person chooses can be changed prospectively.