computations

P:=[0,0,0]; Q:=[1,1,0]; R:=[1,0,1]; S:=[0,1,1];

> with(plots): with(linalg):

> PQ:=scalarmul(Q,t);

> PR:=scalarmul(R,t);

> PS:=scalarmul(S,t);

> QR:=matadd(scalarmul(Q,1-t),scalarmul(R,t));

> QS:=matadd(scalarmul(Q,1-t),scalarmul(S,t));

> RS:=matadd(scalarmul(R,1-t),scalarmul(S,t));

> spacecurve({PQ,PR,PS,QR,QS,RS},t=0..1,view=[0..2,0..2,0..2]);