Added a warm-up

Misc/Warm-Ups/travellers.tex

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+\documentclass[
+	solutions,
+	singlenumbering,
+	nopagenumber
+]{../../resources/ormc_handout}
+\usepackage{../../resources/macros}
+
+\title{Warm-Up: Travellers}
+\subtitle{Prepared by \githref{Mark} on \today}
+
+\begin{document}
+
+	\maketitle
+
+	\problem{}
+	Four travellers are on a plane, each moving along a straight line at an arbitrary constant speed. \par
+	No two of their paths are parallel, and no three intersect at the same point. \par
+	We know that traveller A has met travelers B, C, and D, \par
+	and that traveller B has met C and D (and A). Show that C and D must also have met. \par
+
+	\begin{solution}
+		When a body travels at a constant speed, its graph with respect to time is a straight line. \par
+		So, we add time axis in the third dimension, perpendicular to our plane. \par
+		Naturally, the projection of each of these onto the plane corresponds to a road.
+
+		Now, note that two intersecting lines define a plane and use the conditions in the problem to show that no two lines are parallel.
+	\end{solution}
+
+\end{document}