A function is one-to-one on its domain if the horizontal line {{MATH_181}} intersects the curve {{MATH_182}} in exactly one point, for all values {{MATH_183}} in the range of {{MATH_184}}. This is called the {{CMD_185}}. {{CMD_186}} Below, we give a graph of {{MATH_187}}. While this graph passes the vertical line test, and hence represents {{MATH_188}} as a function of {{MATH_189}}, it does not pass the horizontal line test, so the function is not one-to-one. {{CMD_190}} {{ENV_191}} {{CMD_192}} Although the line {{MATH_193}} intersects the curve {{MATH_194}} exactly once, the function {{MATH_195}} is {{CMD_196}}not one-to-one{{CMD_197}} on its domain, since the line {{MATH_198}} intersects the curve twice.