pub const HELP_SUMMARY: &str = "# Command overview\r\n\r\nThe Calculator provides a minimalistic environment to some math.\r\nIt supports calculation of expressions, definition of function, ploting function\'s and\r\nsolving linar expressions for a given variable.\r\n\r\n## Calculation\r\n\r\nThe calculation supports binary operators normal `+`, `-`, `*`, and `/`.\r\nThe binary `%` calculates the remainder, e.g. `17 % 5` returns `2`.\r\nThe other binary operator is for `^` power, e.g. `3 ^ 2` returns `9` and `3 ^ 4` returns `81`.\r\n\r\nFunctions can be called with the usual syntax, e.g. `abs(-1)` returns `1`.\r\n\r\nVariables are definied with the `:=` operator, e.g. `a := 12`.\r\nSuch a variable can be used in expressions, e.g. `a * 3` returns `36`.\r\nVariables can be redefined.\r\nThe new value is used for the next commands.\r\nCalculator contains build-in constants (see below).\r\nThese constants *cannot* be redefined.\r\n\r\nCustom functions are also defined with the `:=` operator, e.g. `add1(x) := x + 1`.\r\nThese custom functions are called with the syntax above, e.g. `add1(12)` returns `13`.\r\nLike variables custom function can be redefined.\r\nFunctions can have more than one argument, e.g. `sum3(x, y, z) := x + y + z`.\r\n\r\nNote: the `*` operator is not optional.\r\n\r\n### Build-in functions\r\n\r\nThe Calculator contains the following build-in functions:\r\n\r\n- `abs`\r\n- `sin`\r\n- `cos`\r\n- `tan`\r\n- `sinh`\r\n- `cosh`\r\n- `tanh`\r\n- `asin`\r\n- `acos`\r\n- `atan`\r\n- `asinh`\r\n- `acosh`\r\n- `atanh`\r\n- `sqrt`\r\n- `exp`\r\n- `ln`\r\n- `log2`\r\n- `log10`\r\n\r\n### Build-in constants\r\n\r\nThe build-in constants of Calculator are:\r\n\r\n- `e`: Euler\'s constant\r\n- `pi`\r\n\r\n## Ploting functions\r\n\r\nThe Calculator can plot functions with one argument.\r\nThe command starts with the `plot` keyword followed by the function name, e.g. `plot sin`.\r\n\r\nThe plot appears below the command.\r\nIt can be moved and zoomed by touch and/or mouse.\r\nTo move by the mouse point into the graph hold the left mouse button and move the mouse.\r\nTo zoom scroll the mouse.\r\nTo move by touch move one finger in the graph plot and to zoom use the pinch-to-zoom gesture.\r\n\r\n## Solving linear equations\r\n\r\nThe Calculator can solve linear equations with one variable with the `solve ... for ...` syntax.\r\nExample: `solve x = 4 for x` returns `4`.\r\nThe equation may contain function calls, but the dependent variable must not appear in the arguments of the called functions.\r\nOther variables in the equation must be defined.\r\n\r\nA more complex example: `solve 12 * x = 33 + x for x` returns `3`.\r\n";
