If you have'nt played CO-OP yeat and want to play join this group so others can find you to get the Professor Portal Achevement. when you have completed co-op move to the completed group in the link then find some one in this group.

https://steamhost.cn/steamcommunity_com/groups/ProfessorPortalcompleted

NOTE:UNJOIN THIS GROUP WHEN YOU MOVE TO THE OTHER GROUP.

The achevement: Professor Portal
After completing co-op, complete Calibration Course online with a friend who hasn’t played before

NOTE: TO SHOW YOUR READY JOIN GROUP CHAT ON THE 1/2 HOUR SO EVERY ONE FINDS ONE ANOTHER EASYER AND AT THE SAME TIME.