Help needed driving an old PIC programmer from Raspberry Pi GPIO
The 74LS05 is an open collector inverter, therefore it can only output a logic zero on the line (sinking it to the ground), but never a logic one. The line is basically at 1 by default (because of the 10k pull-up resistors) and can be driven to zero either by the inverter output or by the PIC.

Unfortunately, the open collector nature of the 74LS05 is not explicitly indicated in the schematics (although it is possible, generally by putting an asterisk or an open-collector symbol ⎐ near the output of the gate), thus rendering it more difficult to understand.