Jun Maekawa, Gift Box Step 15

[mwp85]

Hello,

I quite new to Origami and are currently working through Jun Maekawas "Genuine Origami". I am stuck at the "Gift Box" Model at step 15. I understand the mountain fold, and I do get the triangle which points downwards, but not the one pointing to the left.

Would anybody be so kind to give me a hint on how to proceed?

Best Regards,
Marcus.